Oxygen delivery systems have been developed for providing supplemental oxygen therapy for a variety of diseases or conditions, such as chronic obstructive pulmonary disease (COPD), respiratory conditions or other medical conditions which require increased oxygen supply to the patient. Supplemental oxygen therapy can be provided using stationary liquid oxygen systems which require a patient to remain stationary during the therapy, which may be required for extended periods of time. Although providing desired therapeutic characteristics, such approaches are undesirable, because they do not allow a patient to have freedom of travel and to function relatively normally. There thus have been developed portable oxygen systems, using small lightweight cylinders of oxygen gas, with offering ambulatory oxygen patients an improve alternative to stationary liquid oxygen systems. Historically, in such portable oxygen systems, oxygen has been supplied to medical patients in a continuous flow, usually administered with cannula or a face mask. Because the human body only needs oxygen during the inhalation phase of the respiratory cycle, oxygen is wasted during the exhalation cycle. This waste of oxygen was also a problem for emergency medical personnel. Ambulatory services were forced to carry larger oxygen tanks that took up limited space and had to be replenished more often. This took time and forced health care professionals to incur unnecessary costs, which in the end were passed on to the patient. In addition, constant exposure to the flow of oxygen tends to dry a patient's nasal passages, causing discomfort and irritation. Due to this, prior art devices were required to humidify the oxygen before it was delivered to the patient which required additional steps and mechanisms at additional costs.
Because of these deficiencies, oxygen conservation devices were developed which deliver oxygen only during the inhalation phase of the respiratory cycle. Generally, these devices function by opening an oxygen supply valve during inhalation and closing the valve during exhalation. These devices drastically reduced the amount of wasted oxygen which meant that smaller, more lightweight tanks could be used.
One important deficiency that still exists in the prior art is that oxygen pressure is assumed to be constant. A high pressure tank of oxygen is fed to a pressure regulator usually designed to output a fixed pressure, typically 20 psi or 50 psi. As the oxygen is depleted from the tank, its pressure will decrease and these fluctuations coupled with less than accurate characteristics of most regulators, results in patients not receiving exact prescribed amounts of oxygen. In addition, calibration of prior art devices is based on the output of the pressure regulator, either 20 psi or 50 psi. Different pressure regulators are not interchangeable without modification to the oxygen delivery controls.
Also in known oxygen delivery systems, a problem has existed in that if the pressure regulator or other components of the delivery system fail, oxygen may not be properly supplied to the patient as required. Such an occurrence could result in a dangerous condition, as the oxygen supply to the patient may be cutoff or may be inadequate for providing the prescribed rate of oxygen required by the patient.
Thus, based upon the foregoing, the performance of oxygen conservation devices or pulse does devices are generally limited by the performance of the available pressure regulators used as a part thereof. As an example, a typical pressure regulator may be a diaphragm regulator, which will regulate oxygen supply within a tolerance band of the regulator, with the output pressure of the regulator affecting the flow rate of oxygen proportionally, such that the supply of oxygen is not constant and precise according to a prescribed oxygen requirement for a particular patient. In the example of a diaphragm regulator, the regulated pressure output may be selected to be 20 psi, with the actual amount of oxygen delivered varying between 17 psi to 23 psi assuming a plus or minus 15% tolerance in the regulator. In such an example, if a patient is prescribed 5 L/min. of oxygen, the patient may receive anywhere between 4 L/min. to 6 L/min. of oxygen, depending on the pressure of the source of compressed oxygen gas. In another aspect, oxygen delivery systems provide a predetermined volume of oxygen per period of time for an inhalation phase of the respiratory cycle. Such an approach assumes that the oxygen required by the patient remains constant, not accounting for changes in the breathing cycle of the patient.
Therefore, in light of the foregoing deficiencies in prior art oxygen delivery systems, a need exists for an oxygen delivery system which can deliver precise doses of oxygen to a patient in a prescribed amount regardless of characteristics of a pressure regulator or changes in the patients respiratory cycle.